Cities Getting Ready for Next Heat Wave

Cities getting ready
for next heat wave

Results applied from
Urban Heat Island Pilot Project

November 20,
1998: As the first chills of autumn erase the memories of
this summer's heat wave, three cities are starting to apply lessons
from sweltering portraits painted by a NASA-led team of Earth
scientists.

Salt Lake City is figuring out how to keep the air clean for
the 2002 Summer Olympics, and Baton Rouge and Sacramento are
planning where to plant trees.

Right: Sacramento
displays a little of everything, from blistering railyards to
the cool California River, in visible and thermal infrared images.
Detailed images are
available below. Credits for all photos: NASA/Marshall Space
Flight Center.

These new efforts come as a result of data from the Urban
Heat Island Pilot Project (UHIPP) which coordinated observations
by ground teams with airborne and satellite sensors and cameras
of the three "pilot cities:" Baton Rouge, Louisiana,
May 18; Sacramento, California, June 29; and Salt Lake City,
Utah, July 13 and Sept. 15 (a second flight because of instrument
problems on the first flight). Several other U.S. cities participated
through ground-based and satellite observations. Atlanta was
studied in May 1997.

Teaming with NASA's Marshall Space Flight Center in the pilot
project were the U.S. Environmental Protection Agency (EPA),
the U.S. Department of Energy, the Lawrence Berkeley National
Laboratory, Baton Rouge Green, the Sacramento Tree Foundation,
Tree Utah, and the Utah State Energy Services Department.

The ultimate objective of the EPA, UHIPP's principal funding
agency, is improving air quality, specifically by reducing ozone.
The overall goal of this project is finding ways to cool the
city and thereby reduce ozone pollution problems.

Although most science projects take months to complete, and
even longer to produce results, the UHIPP team is pushing to
get the data out to city planners by year's end.

Starting this month, NASA and the EPA are working with the
Pilot Cities to develop "Action Plans" that will: 1)
categorize land use across the city; 2) estimate the areas of
maximum potential for reflective surfaces and urban afforestation;
3) identify which organizations within the city or a given community
would be appropriate in helping to implement the mitigation measures;
and 4) outline and prioritize policy levers and potential programs
that offer the largest cooling potential at the least cost.

"This is not a research project," said the study's
lead investigator, Dr. Jeff Luvall of Marshall Space Flight Center's
Global Hydrology and Climate Center. "We want to get the
data out to city planners as soon as possible." The raw
data sets will be about 2 to 3 gigabytes per city. That will
swell when the data are fully calibrated to correct for atmospheric
interference and apply laboratory optical bench calibrations
to the instruments.

The basic concept behind UHIPP can be felt on a hot day when
you drive from city canyons to wooded areas: it gets cooler.

"While UHIPP is quite complex," Luvall explained,
"at its core is the fact that the evaporation of water absorbs
a lot of heat. Plants, and trees in particular, evaporate large
amounts of water from their leaves. The energy required to evaporate
water is taken from the air and from the sunlight intercepted
by the leaves, thus cooling the air. Trees are also very effective
in shading the ground, thus preventing the heating of the surface
by sunlight."

On the other hand, asphalt, concrete, and other manmade materials
are very effective at absorbing light and reradiating it as infrared
radiation that raises the temperature of the air. In turn, that
makes air conditioning systems work harder, even after sunset.
As a result, utility bills go up and heat stress as a result
of increased heat over the city can affect human health.

Atop all that, depending on weather conditions, the hot air
will form a dome or bubble over the city which is several degrees
warmer that the surrounding countryside.

Feeling cooler is a nice feeling, but city planners need hard
data to help justify changes in how things are done. Thus, UHIPP
is providing a series of demonstrations.

The bird's eye view

While weather satellites and ground observers
played important roles in UHIPP, the key instruments were the
Advanced Thermal and Land Applications Sensor (ATLAS) and a 23x23
cm (9x9 in) film camera carried aloft by a NASA Lear 23 jet (above)
operating from Stennis Space Center. ATLAS - basically the same
as the main camera aboard the Galileo spacecraft - sees in 15
distinct wavelengths. It readily shows concrete and asphalt glowing
bright in thermal infrared, while trees and other vegetation
are darker because the sun's energy is being dissipated mostly
through the evaporation of water from their leaves. The film
camera provided visible images to match hot and cold spots with
known objects on the ground. Links to 919x447-pixel,
382KB JPG.

A UHIPP sampler

The images below are visible (left) and thermal
infrared (right) sections from the larger images covering each
city. Because each image has not been calibrated, absolute temperatures
will change after calibration, but the relative temperature differences
between surface types will not.

Baton Rouge, La.:The
yellow and red areas are hot, and generally correspond with roads
and buildings; blue and green areas are cool and indicate water
and vegetation. The bright red areas in this image are about
65 deg. C (149 deg. F); dark green and blue areas are around
25 deg. C (77 deg. F). The solid blue swatch of color flowing
down the left side is the Mississippi River. Links to 600x300-pixel,
227K JPG. Click here for the entire city in a 1600x977-pixel,
1.8 MB JPG.

Sacramento, Calif.: The
white areas, mostly rooftops, are about 122 deg. C (140 deg.
F) and the dark areas are approximately 29-36 deg. C (85-96 deg.
F). The hottest spots are buildings, seen as white rectangles
of various sizes. Sacramento's rail yard is the orange area east
of the Sacramento River, which flows from top to bottom. In the
complete image, the state capitol is the red spot in the green
rectangle to the right center of the river. Links to 600x300-pixel,
227K JPG. Click here for the entire city in a 1600x979-pixel,
2 MB JPG.

Salt lake City, Utah:
Again, the yellow and red areas are hot and generally correspond
with roads and buildings; blue and green areas are cool and indicate
water and vegetation. The white areas are about 71 deg. C (160
deg. F); blue and green areas are approximately 29-36 deg. C
(85-96 deg. F). The complete image spans Salt Lake City from
about 300 West Street on the left edge of the image, to the foothills
of the Wasatch Mountains on the eastern edge. Links to 600x300-pixel,
235K JPG. Click here for the entire city in a 1661x977-pixel,
2 MB JPG.

"We're starting to develop sample data sets, even though
they're not fully calibrated, to get the feel for how to handle
it," Luvall said. The data packages will include public
domain software and low-cost geographic information systems to
help city planners map the data onto specific parts of their
cities.

"The sooner we can get the data out to the people, the
quicker they can learn how to deal with it when the calibrated
sets are available," Luvall said.

Already, the preliminary results are having an effect.

Salt Lake
City is using the early results to help plan sites for the 2002
Winter Olympic Games and develop strategies to reduce ground-level
ozone concentrations in the Salt Lake City valley. Not to be
confused with the "good" ozone layer protecting Earth
from ultraviolet rays, ground-level ozone is a powerful and dangerous
respiratory irritant found in cities during the summer's hottest
months.

In Sacramento and Baton Rouge, city planners and tree planting
organizations are using the study to focus their tree-planting
programs.

"We are helping the cities incorporate the study into
their urban planning," said Maury Estes, an urban planner
with the Universities Space Research Association and a part of
the science team at NASA/Marshall. "By choosing strategic
areas in which to plant trees and by encouraging the use of light-colored,
reflective building material, we think that the cities can be
cooled."

Meanwhile, UHIPP data are being used by Luvall and his colleagues,
and by scientists at the Lawrence Berkeley National Laboratory,
to produce computer models so planners from other cities can
better predict the heat island effect for their cities, and then
plan remedies.